Getting Closure: Exposing the Eyelid Overbite

28 11 2012

Blinking has always been known to have 2 purposes: 1) to clear away debris from the tear film and 2) to replenish the tear film to allow the cornea to remain a clear optical surface.  When we sleep, conventional wisdom suggests that the eyelids meet halfway and form a seal that prevents exposure of the cornea throughout the night.  Nocturnal lagophthalmos is an anatomical state whereby the superior and inferior lids fail to meet resulting in exposure of the conjunctival and corneal surfaces at night.  These patients typically present with symptoms of persistent dry eyes, recurrent corneal erosions, and often have a psychological impact due to constant questioning of their red eyes by family, friends and co-workers alike.   There is evidence that suggests that in the general population 1.4% of patients have some form of lagophthalmos.

A deeper look at the finer anatomical structures of the eyelid suggest that our blinks have a different purpose, and in fact may not be as efficient at closing the gap on our dry eyes.

Figure 1. Gross anatomy of the eyelid

The lids meeting is contingent on the anatomical reach of of lids, but as important is the seal created by the meeting of the superior and inferior line of Marx (LOM).   With reduction in lid laxity with age, changes in lid tension by blepharoplasty and less frequent and deliberate blinking with computer/smartphone/tablet use this ‘seal’ is not always present.  The result is an eyelid overbite, where the upper eyelid falls slightly anterior to the lower eyelid causing the LOM’s to miss each other and therefore no true touching of the upper lid to the lower lid.  An often overlooked function of the blink is to create a negative pressure to draw meibum or oil out of the meibomian glands (MG) when the lids touch.  If they don’t touch, then this negative pressure cannot stimulate expression of the oil from the gland and will create an oil deficient eye, susceptible to evaporative dry eye (EDE).  Over time, inactivity or reduced activity of the MG will result in stagnation of meibum and MGD ensues. Clinically, we can see this in various degrees within the symptomatic patient, however the asymptomatic patient has signs as well.

How can a practitioner determine if the lids are meeting microscopically?  Using a slit lamp and looking for smile staining on the cornea/conjunctiva  means looking for chronic signs of exposure, which aren’t always there in the early stages.  There is an onset of physiological changes within every disease and a simple use of a transilluminator will reveal a very telling sign.  Dr. Donald Korb OD FAAO, has used this technique in practice for years and it is now incorporated into every consultation I see in my dry eye clinic.  The example below demonstrates  the ‘light leakage’ sign indicating a break in the seal of a blink.  On SLE, this patient appears to have good closure and no obvious staining patterns were associate, however she presented with severe dry eye symptoms but normal aqueous production.  On identification of the broken seal, she was tested for non-obvious MGD (NOMGD) and lid wiper epitheliopathy (LWE) which was confirmed.

Figure 2. Leaking Light – sign of incomplete lid seal between upper and lower eyelid

This is the eye-equivalent of an overbite and is a telling indicator of exposure and potential future MG dysfunction.  These patients benefit from exposure therapy such as moisture chamber goggles, hyper-viscous topical agents at night, manual lid expression and regular assessment of the lid wiper and line of Marx for epithelial changes and accumulation.  Compression on the lid of  these patients should be done with caution as fine debris can enter the broken seal and abrade the cornea as well patients should be educated on corneal warpage post compression.

The micro anatomy and complex coordination of a blink can and in fact does break down with age, cosmetic surgery and with environmental factors.  Closer evaluation of the lid surface as it relates to chronic disease progression doesn’t require symptoms to be present.  The role of the primary eye care physician is to provide front-line care which helps in the prevention of eye disease.  Dry eye, having a population of 100 million globally , as stated by TFOS in 2011 may have it’s roots firmly planted in the lid.

In good health,

Dr. Richard Maharaj OD, FAAO

rmaharaj@eyelabs.ca

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